Figure 2.

Curve of ${\displaystyle I_1^{†}}$ as a function of ${\displaystyle u_1}$ using Lesotho and Indonesia data in panels (a) and (b), respectively. ${\displaystyle P_1}$ is the turning point of ${\displaystyle I_2^{†}}$ , while ${\displaystyle P_2}$ is ${\displaystyle u_2}$ when ${\displaystyle {\mathcal{R}}_c=1}$ . When ${\displaystyle {\displaystyle u_1<u_1^{\ast }}}$ , then ${\displaystyle I_1^{†}}$ increases as ${\displaystyle u_1}$ increases. The critical value ${\displaystyle u_1^{\ast }}$ for Lesotho and Indonesia is 0.308 and 0.398, respectively. TB-endemic equilibrium only exists when ${\displaystyle {\displaystyle u_1<P_2}}$ .